Just curious; what's the chance of damaging the phone by "cranking out" too much voltage? Other than that I really like this idea. I suppose if you're stuck somewhere and your phone is dead and you have an emergency and you have no other way of charging the phone AND you just happen to have a rechargeable drill with the right equipment to pull this off it's worth the risk of damaging your phone. I'm more interested in how this could be applied to charging larger batteries such as lead-acid car batteries. Also, this makes me wonder what other devices I might have around the house that I could convert into electrical generators in a pinch.

Thanks for your feedback and your question. I believe this would actually work better for charging larger lead-acid type batteries. Higher voltage batteries would require spinning the drill faster so maybe it could be hooked up to a bicycle to accomplish that. I didn't notice any damage to my phone from doing this, but my goal was to just spin it barely fast enough to get the charging symbol. That was my safeguard against over voltage. I hope that helps!